I'm just gonna throw out there the fact that modern homo sapiens do have some neanderthal DNA, as far as we can tell, and we've gotten some talk about how producing fertile offspring makes you technically the same species.
To be honest, I would prefer this series either said "yup, they're all dead and Taiga's got to live life on his own" or stopped teasing us with "are they alive? Where are they? Let's go find them!" by having a reunion pretty damn fast. I like both those potentials better than dragging the current state along much longer.